//go:build linux

package main

import (
	"os"
	"path/filepath"
	"strings"
)

const powerSupplyRoot = "/sys/class/power_supply"

func systemBattery() (bool, error) {
	return sysfsOnBattery(powerSupplyRoot)
}

func readSupplyField(dir, name string) string {
	data, err := os.ReadFile(filepath.Join(dir, name))
	if err != nil {
		return ""
	}
	return strings.TrimSpace(string(data))
}

func isMainsType(kind string) bool {
	return kind == "Mains" || kind == "ADP" || strings.HasPrefix(kind, "USB")
}

func sysfsOnBattery(root string) (bool, error) {
	entries, err := os.ReadDir(root)
	if err != nil {
		return false, err
	}
	discharging := false
	for _, entry := range entries {
		dir := filepath.Join(root, entry.Name())
		if readSupplyField(dir, "scope") == "Device" {
			continue
		}
		kind := readSupplyField(dir, "type")
		switch {
		case kind == "Battery":
			if readSupplyField(dir, "status") == "Discharging" {
				discharging = true
			}
		case isMainsType(kind):
			if readSupplyField(dir, "online") == "1" {
				return false, nil
			}
		}
	}
	return discharging, nil
}